Perfluoropolyether compounds have excellent heat resistance, chemical resistance, and oxidation resistance, and also have a high viscosity index such that they have relatively stable (unchanging) fluidity (viscosity) across a wide temperature range from low temperatures to high temperatures and exhibit good lubricity. Further, perfluoropolyether compounds are nonflammable, have almost no impact on polymer-based materials such as rubber and plastics, and have other characteristics such as low vapor pressure and evaporation loss, low surface tension, and high electrical insulation.
As described above, perfluoropolyether compounds are known to exhibit high performance as a lubricant across an extensively wide range of applications. As such, perfluoropolyether compounds are widely used in vacuum pump oil as lubricating oil, a lubricant for a magnetic disk/tape or the like, a heat medium, a non-adhesive, and various other applications.
On the other hand, C60, which is a type of fullerene, is known to be useful as a lubricant.
Non-Patent Literature Document 1 indicates that a silicon substrate having a C60 deposited film formed thereon exhibits a lower friction coefficient. Non-Patent Literature Document 1 also describes a fullerene derivative obtained by introducing a perfluoropolyether group into a fullerene. However, the above documents provide no description of specific compounds or their production methods.
Also, C60 is known to exhibit excellent properties as an additive to conventional lubricants.
Non-Patent Literature Document 2 indicates measurements of the frictional resistance of a copper foil surface coated with an ordinary lubricating oil and a copper foil surface coated with the lubricating oil that has 5% of C60 added thereto. The frictional resistance was measured by rubbing a steel roller while applying a load. The measurement results indicated that the frictional resistance improves when C60 is added, as compared with the case where C60 is not added.
Patent Document 1 describes a lubricant composed of a mixture of a fullerene, a fullerene derivative having a carboxyl derivative or an ester group of the fullerene, and a perfluoropolyether compound.
Patent Document 2, Patent Document 3, and Patent Document 4 describe a fullerene derivative having one perfluoropolyether group in the molecule as an n-type semiconductor material.
However, Patent Document 2, Patent Document 3 and Patent Document 4 do not describe the application of the fullerene derivative in a lubricant.
Patent Document 5 and Patent Document 6 describe a lubricant composed of a derivative in which one perfluoropolyether group is provided for each cyclopropane ring that is condensed to a fullerene.
Note that owing to the modification of the fullerene, the lubricant described in Patent Documents 5 and 6 exhibit improved abrasion resistance as compared with the lubricant described in Patent Document 1. However, further improvement in abrasion resistance is desirable.
Patent Document 7 describes a lubricant composed of a fullerene derivative in which two perfluoropolyether groups are provided for each cyclopropane ring that is condensed to a fullerene.
As with the lubricant described in Patent Documents 5 and 6, further improvement in abrasion resistance is desirable with respect to the lubricant described in Patent Document 7.